Roller bearings, such as ball bearings, are used to reduce friction between components that are intended to have relative rotation. A set of rollers separate an inner ring from an outer ring. Relative rotation of the inner ring and outer ring causes rolling contact, as opposed to sliding contact, between the roller and the inner ring and between the rollers and the outer ring. Substantial radial forces may be transferred through the rollers with minimal drag torque.
In some roller bearings, the rollers are circumferentially positioned relative to one another by a bearing cage. The bearing cage rotates at a speed approximately equal to an average of the speeds of the inner ring and the outer ring.